SU82543A1 - Automatic electromagnetic switch - Google Patents

Description

Various schemes are known for protecting the asynchronous motors with a short-circuited rotor winding during their start-up, which automatically bypass the fuses, thus preventing them from overheating under the action of in-rush currents.

The use of such devices in a number of cases, for example, for electric drives of pumping units in the oil and gas industry, is of great importance. However, such devices with relatively high current increases, shunt fuses, exclude motor protection against overload.

In the proposed circuit breaker, the action of which is also based on the price of automatic fuses, this drawback is eliminated. Along with this, an automatic shutdown of the electric motor is also provided when one of the fuses blows, carried out according to the known scheme of parallel connection of the tripping coils to the fuses. To shut off the engine with a prolonged start-up of dangerous starting currents, the current relay used to knock down their fuses is provided with a time delay element acting on the opening electromagnet.

FIG. 1 shows the principal circuit breaker; in fig. 2-option scheme.

The three-pole contact system of the switch / is connected to the traverse 2. which, when the switch is turned on, is locked by the latch 3. It is equipped with an electromagnet e with two coils 4 and 5, connected in parallel to the fuse1 M of the bodies 6 and 7, serving to protect the engine from overload.

The cutters are designed for short-term work, therefore, their overall dimensions are very small. In parallel with the coils, there are instantly acting shunting contacts 8 c 9 of a special relay, equipped with a current coil 10. The latter is connected in series in one phase of the electric motor.

The core 11 of the current relay is connected by means of a spring 12 to a time delay mechanism 13, which acts on the contacts 14 and 15 included in the coils 4 of the electromagnet.

No. 82543-2 Normally, contacts 15 hold coil 4 in a state of parallel connection 10 with respect to fuse 6. In the event of a current relay, after a period of 6-7 seconds, contacts 15 open, and contacts 14 turn on coil 4 between two phases.

The relay current is chosen such that the relay pulls in its heart to two times the rated motor current.

The switch of the circuit breaker is operated with a knob associated with ,,,, Lree turning the latch 5 into engagement with the crosshead 2 and holding the switch in the on state.

The starting current of the motor, the passage through the coil 10 of the current time relay, causes the core to be drawn in and the contacts are instantaneously active (S and 9 are closed. Due to this, fuses 6 and 7, which are not designed for starting current, are short-circuited and thereby prevent them from burning out start.

During the normal course of the engine starting process, the current in the coil 10 drops to the nominal value after more than 3-4 seconds, after which the core of the relay returns to its original position, contacts 8 VI 9 open and fuses 6 and 7 are inserted into the engine circuit.

If one of the fuses blows, a current enters the corresponding coil 4 or 5 of the electromagnet, as a result of which the latch 5 trips and the switch turns off the engine.

During normal operation, if the motor is overloaded for reasons or reasons (for example, from a strong decrease in the mains voltage or from an overload driven by the machine-machine) with a current exceeding the set value of the current relay, the latter will take effect and after a set period of time ( 6-7 sec), will switch the coil of the 4 electromagnet to the full power network, which will cause the automatic switch off of the switch. If the duration of the overload is shorter than the set time delay, the switch will not turn off and the engine will remain in operation.

The described action of the current relay and the switching off of the circuit breaker will also occur when the motor is started too long, when the latter fails to turn around within a 6-7 sec control period. This circumstance is very important when drying, self-starting electric drives, when the automatic start of engines occurs in the absence of maintenance personnel. From this point of view, the application of the proposed switch is of particular practical importance for the electric drives of pumping units in the oil industry.

For zandity from short-circuit currents in front of the switch are installed (as with magnetic starters) fuses, designed for four times the rated current.

The circuit variant given in FIG. 2, differs from the described one only in that in what, instead of the electric connection, the mechanical / connection of the interlock 3 with the time-delay mechanism 13 is made.

Subject invention

Automatic electromagnetic switch for protection of asynchronous electric motors with a short-circuited rotor winding, equipped with fuses designed for overload current, and a current relay for shunting fuses during the start-up period, characterized in that, in order to realize a complete shutdown of the engine during a continuous start, also in case of severe overload or single-phase power supply, the current relay is equipped with a time delay element acting on a tripping electromagnet equipped with two coils connected in parallel with fuses of different phases.